Conventionally, in various cameras and cellular phones with cameras having zoom functions, a piezo motor or an actuator comprising a magnet and a coil together is used to drive a lens and a position detecting device (sensor) is used in order to determine a position of the movable lens or the like.
For example, as described in Patent Document 1 and 2, a device for detecting a lens located not less than 5 mm apart from a sensor using the above actuator is generally configured such that magnets are arranged over a plurality of magnetic sensors such as MR elements (magnetic resistive effect elements) or hall elements, and the magnets have a size covering these elements. Therefore, the device itself becomes large-scale. In an application in which such a position detecting device is used, when another component producing a magnetic field is used, the position detecting device can sometimes actuate incorrectly due to influence of interaction between the magnetic fields.
Therefore, it has been demanded to configure a position detecting device using a reflection type photosensor. In a conventional position detecting device using a reflection type photosensor, one reflection type photosensor is used on an actuator for detecting an autofocus lens of a cellular phone in order to detect a position of a lens located not more than 1 mm apart from the reflection type photosensor. For example, the configuration, as shown in FIG. 7, a reflection type photosensor 51 is provided with opposing to a mirror 52 fixed on a movable body; outputs of the reflection type photosensor 51 to distance d between the reflection type photosensor 51 and the mirror 52 (position of the movable body) are detected when the movable body moves, and are converted from analog data to digital data, and the relation of the outputs and the distance is stored in a memory; and a distance d of the movable body is measured by comparing the outputs of the reflection type photosensor 51 and the data of the memory. The relation of the distance d and the output of the reflection type photosensor 51 shows a curve line as shown in FIG. 8, for example. To obtain accurate values of the position of the movable body, parts with comparatively stable and significant difference (a part of the arrow P in FIG. 8) only can be used. Accordingly, a part with the distance d being comparatively shorter in which the output sharply changes (less than 0.5 mm of distance d) or a part with low sensitivity in which the output almost no changes (not less than 1.3 mm) can not be used to detect the accurate positions.
In other methods using a reflection type photosensor, the reflection type photosensor is arranged such that surfaces of a light emitting element and of a light receiving element of the reflection type photosensor are aligned parallel to a moving direction of the movable body, and then positions of edge parts of the movable body are measured. However, the method has similar sensitivity to the above method and can measure only about 1 mm or less.